Love on the rocks: Penguins celebrating Valentine's Day

In what has become an annual Valentine's Day tradition, biologists handed out red felt hearts to the 14 African penguins at the California Academy of Sciences on Tuesday.

The animals grabbed the hearts in their beaks and waddled around their rocky enclosure toward their nests.

Spokeswoman Kelly Mendez said it is often the male penguin who retrieves the heart and carries it back to his mate. The penguins use the felt for material in their nests, which helps reinforce the couples' bonds.

The activity is part of the academy's captive breeding program to help increase the African penguin population, which is endangered in the wild.